The long-term objective of this project is to discover basic principles concerning the detection and discrimination of odorant mixtures and their componets. The focus of this research will been responses to bianry odorant mixture, which will serve as a model for more complex mixtures. A common observation in studies of mixtures of odorant or tastants is that responses to mixtures are often not predictable, even when thresponses to the individual components of the mixtures are known. These phenomena, termed mixture interactions, are widespread, occurring in humans as well as lower animals. The proposed project uses as the experimental animal model the spiny lobster Panulirus argus, which has proven to be an excellent system for studies of olfaction, including mixture interactions and behavioral and neural aspects of quality coding. The specific aims of this project are to: (1) identify and characterize olfactory mixture interactions for binary odorant mixtures; and (20 evaluate the effects of mixture interactions on behavioral and neural discrimination of the quality of banner odorant mixtures. Mixture interactions will be identified and characteri by appealing behavioral models of ligand-receptor binding. The effects of mixture interactions on discrimination of quality of bianry odorant mixtures and their components will be described btu evaluating quality discrimination for bianry mixtures containing componets that door do not show mixture interactions, using previously developed techniques;: multivariate analysis of single-unit neurophysiological data from olfactory receptor cells and olfactory brain interneurone for neural discrimination; multivariate analysis of results of differential aversive conditioning for behavioral discrimination.